Copper-clad iron conducting rod and preparation method thereof

Abstract

The invention discloses a preparation method of a copper-clad iron conducting rod, which comprises the following steps of: covering a copper pipe on an iron rod with a metal transition layer on the surface, and then performing multi-pass cold drawing composite treatment to obtain a composite rod; and then annealing to obtain the copper-clad iron conducting rod. The invention further discloses the copper-clad iron conducting rod which is manufactured according to the method. An iron rod is adopted as a core material to provide structural strength, a micron-sized metal transition layer is formed on the surface of the iron rod through electroplating, a copper pipe is sleeved and covered to serve as a conductive layer, interface metallurgical bonding is achieved through multi-pass cold drawing, annealing treatment is conducted in a reducing atmosphere, and the comprehensive performance is synergistically improved through an interface bonding mechanism and material performance; the design of the transition layer solves the copper-iron interface bonding problem, the copper pipe and the multi-pass cold drawing technology are used for guaranteeing the conductivity, the cost control is achieved by means of the iron rod, and the problems that in a traditional process, the bonding strength is insufficient, the oxygen content is high, and the technological process is complex are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of conductive element manufacturing technology, and in particular to a copper-clad iron conductive rod and its preparation method. Background Technology

[0002] Conductive rods are key components in power transmission, rail transportation, metallurgy, and chemical industries, requiring high conductivity, high strength, and good durability. Currently, mainstream conductive rods on the market are mainly made of pure copper. Pure copper conductive rods have extremely high conductivity, but they suffer from drawbacks such as high cost, low mechanical strength, and high density. To reduce costs and improve strength, composite conductive materials such as copper-clad steel or copper-clad aluminum have emerged in existing technologies. However, copper-clad aluminum suffers from a large potential difference between copper and aluminum, making it prone to electrochemical corrosion in humid environments. Furthermore, aluminum has a low melting point, posing a higher risk during overload or short circuits. Traditional copper-clad iron technology often employs processes such as sheathing followed by drawing or explosive bonding, which suffers from weak bonding between the copper layer and the iron core, easy oxidation at the interface, and easy delamination, severely affecting conductivity stability and service life. In addition, existing copper-clad iron technologies, such as electrodeposition, suffer from limited copper layer thickness, high oxygen content, and low production efficiency; while hot processing composite processes (such as hot extrusion and hot spinning) face challenges such as expensive equipment, the need for a reducing atmosphere for protection, unsuitability for mass production, and the risk of high-temperature oxidation. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, this invention proposes a copper-clad iron conductive rod and its preparation method. This invention uses an iron rod as the core material to provide structural strength. A micron-level metal transition layer is formed on the surface of the iron rod by electroplating. A copper tube is then wrapped around the iron rod as a conductive layer. The interface metallurgical bonding is achieved through multiple cold drawing processes, and annealing is performed in a reducing atmosphere. This allows the interface bonding mechanism and material properties to be synergistically improved, resulting in a comprehensive performance enhancement. The transition layer design of this invention solves the problem of copper-iron interface bonding. The use of copper tubes and multi-pass cold drawing technology ensures conductivity. Cost control is achieved by using iron rods. This forms a complete and reliable large-scale production process for copper-clad iron conductive rods, effectively overcoming the technical bottlenecks of insufficient bonding strength, high oxygen content, and complex process flow in traditional processes.

[0004] This invention proposes a method for preparing a copper-clad iron conductive rod, comprising the following steps: covering an iron rod with a metal transition layer on its surface with a copper tube, then performing multiple cold drawing composite treatments to obtain a composite rod; and then annealing to obtain the copper-clad iron conductive rod.

[0005] The iron rods are subjected to degreasing, pickling, and activation treatments in sequence before electroplating.

[0006] Oil can be removed using alkaline solution; the oil removal conditions can be: in a mixed aqueous solution of sodium carbonate and trisodium phosphate with a total concentration of 30-50 g / L, oil removal is carried out at 60-80℃ for 10-20 min.

[0007] Pickling conditions can be as follows: soak the iron rod in a 10-15 wt% sulfuric acid or hydrochloric acid aqueous solution at room temperature until the surface of the iron rod is uniformly silvery-white, with a soaking time of 3-8 minutes.

[0008] The activation conditions can be to immerse the sample in a 5-8 wt% hydrochloric acid aqueous solution at room temperature for 30-60 s, and then immediately transfer it to an electroplating tank.

[0009] The copper tube is assembled by gently sliding it in.

[0010] Preferably, the iron rod is made of low-carbon steel or low-alloy high-strength steel.

[0011] The aforementioned low-carbon steel refers to carbon steel with a carbon content of less than 0.25%.

[0012] The aforementioned low-alloy high-strength steel refers to a type of engineering structural steel developed by adding small amounts of Mn, Si, and trace amounts of alloying elements such as Nb, V, Ti, and Al to carbon structural steel.

[0013] Preferably, the low-alloy high-strength steel contains chromium and vanadium.

[0014] Preferably, the metal transition layer is made of nickel or copper.

[0015] Preferably, the thickness of the metal transition layer is 1-3 μm.

[0016] When the metal transition layer is too thin, its role as a diffusion barrier and stress buffer will be difficult to play, and it will be unable to effectively prevent iron atoms from migrating to the copper layer and the interface from oxidizing, resulting in a significant decrease in bonding strength and easy delamination during subsequent processing or use. When the metal transition layer is too thick, it will not only increase production costs and time, but may also induce cracking or peeling due to increased internal stress. At the same time, an excessively thick transition layer (such as nickel) will also slightly reduce the overall conductivity due to its inherent resistivity.

[0017] Preferably, a metal transition layer is prepared on the surface of the iron rod by electroplating.

[0018] When the aforementioned metal transition layer is made of nickel, the electroplating conditions are as follows: the concentration of nickel sulfate in the plating solution is 200-250 g / L, the pH value of the plating solution is 3.5-4.5, the temperature of the plating solution is 50-60℃, and the cathode current density is 1-3 A / dm³. 2 The electroplating time is 5-10 minutes; When the aforementioned metal transition layer is made of copper, the electroplating conditions are as follows: the concentration of copper pyrophosphate in the copper plating solution is 70-90 g / L, the pH value of the copper plating solution is 8.2-8.8, the temperature of the copper plating solution is 50-55℃, and the cathode current density is 0.5-1.5 A / dm³. 2 The electroplating time is 8-15 minutes.

[0019] The above-mentioned nickel plating solution is a Watts-type nickel plating solution, which refers to a sulfate-type (low chloride) nickel plating solution. The above-mentioned copper plating solution is an environmentally friendly pyrophosphate copper plating solution.

[0020] The above-mentioned Watts-type nickel plating solution may contain: 200-250 g / L nickel sulfate, 30-60 g / L nickel chloride, 30-40 g / L boric acid, etc.

[0021] The aforementioned nickel plating solution and copper plating solution can be purchased from the market.

[0022] Preferably, the copper tube is made of oxygen-free copper.

[0023] Preferably, the oxygen content of the oxygen-free copper is ≤100 ppm.

[0024] Preferably, the single-sided gap between the inner diameter of the copper tube and the diameter of the iron rod with a metal transition layer on the surface is 0.05-0.15 mm.

[0025] Preferably, the wall thickness of the copper tube is The copper layer thickness of the composite rod is , .

[0026] Preferably, the copper layer thickness of the composite rod is [missing information]. The radius of the composite rod is R. .

[0027] In the aforementioned composite rods and copper-clad iron conductive rods, the copper layer thickness is the same. If the copper layer thickness of the copper-clad iron conductive rod is too thin, the current conduction cross section will be mainly borne by the iron core with high resistivity, resulting in a sharp deterioration in the overall conductivity and defeating the original purpose and advantages of using a copper-clad structure. If the copper layer thickness of the copper-clad iron conductive rod is too thick, although it can improve conductivity, its gain will gradually approach saturation, while the high cost of copper will increase linearly, significantly reducing the product's cost-effectiveness. At the same time, the contribution of an excessively thick copper layer to the overall strength of the conductive rod becomes negligible, failing to fully utilize the high strength characteristics of the iron rod.

[0028] Multi-pass cold drawing composite treatment, through plastic deformation, enables the copper tube and iron rod to achieve a strong metallurgical-mechanical bond, resulting in a composite rod.

[0029] Preferably, the number of cold drawing passes is 3-6.

[0030] Preferably, during the multi-pass cold drawing composite process, the total cross-sectional shrinkage rate is 30-50%.

[0031] Preferably, in the multi-pass cold drawing composite process, the cross-sectional shrinkage rate of the initial pass is 15-20%, and the cross-sectional shrinkage rate of each subsequent pass decreases to 5-10%.

[0032] The cross-sectional reduction rate for each pass refers to the ratio of the difference in cross-sectional area of ​​the composite bar before and after each pass to the cross-sectional area of ​​the composite bar before each pass.

[0033] Adjusting the initial cross-sectional reduction rate appropriately can ensure that the interface achieves an effective initial bond. The cross-sectional reduction rate of subsequent passes decreases gradually, which can smoothly reduce the diameter and control work hardening.

[0034] Preferably, in the multi-pass cold drawing composite process, the drawing force F in each pass is... k × s × A × ln (A 0 / A 1 ) ,in, k For safety factor, k The value ranges from 1.1 to 1.3. s The average flow stress of the copper-iron composite material. s The value ranges from 350 to 500 MPa. A 0 、A 1 These are the cross-sectional areas of the composite rods before and after each pass. A= ( A 0 +A 1 ) / 2.

[0035] The above copper-iron composite material s The value is mainly dominated by the work hardening of copper. Based on the deformation per pass, the typical range is 350-500 MPa, which can be found from the stress-strain curve of pure copper.

[0036] The unit of the pull-out force F mentioned above is kN. A The unit is mm 2 .

[0037] Choosing the appropriate pull-out force is the fundamental guarantee for achieving a strong composite interface and precise geometric dimensions in copper-clad iron conductive rods. Its main advantage lies in providing sufficient and uniform radial pressure, forcing the copper layer and iron core to undergo coordinated plastic flow, achieving atomic-scale close contact and initial diffusion at the interface, thus forming a high-strength metallurgical bond; simultaneously ensuring uniform axial diameter reduction of the composite rod, obtaining precise diameter and copper layer thickness.

[0038] If the drawing force is too small, the interfacial pressure will be insufficient, resulting in low bonding strength, easy delamination, and poor airtightness; if the drawing force is too large, it is very easy to exceed the plastic limit of the material (especially the outer copper layer), causing a breakage accident or serious damage to the drawing die, resulting in production interruption and cost waste.

[0039] Under the premise of ensuring effective transfer of drawing force and full bonding of the interface, an appropriate drawing speed can maximize output per unit time and reduce production costs. At the same time, a suitable speed helps to reduce the risk of frictional heat accumulation and surface scratches, thereby obtaining a bright and dense rod surface. If the drawing speed is too fast, it will cause surface "roughness" or scratches, and excessive deformation heat may induce local softening or oxidation of the copper layer; if the speed is too slow, it will lead to low production efficiency.

[0040] Preferably, the drawing rate for each pass is 2-5 m / min.

[0041] Preferably, annealing is performed in a protective gas atmosphere.

[0042] Preferably, the dew point of the protective gas is ≤-20℃.

[0043] Preferably, the protective gas is hydrogen or hydrogen produced by the decomposition of ammonia.

[0044] Preferably, the annealing temperature is 400-500℃ and the annealing time is 30-60 min.

[0045] Preferably, the temperature is increased to 400-500℃ at a rate of 5-15℃ / min.

[0046] After the above annealing, the furnace is cooled to room temperature to obtain a copper-clad iron conductive rod.

[0047] The above-mentioned annealing can eliminate processing stress, reduce oxygen content, and promote the interdiffusion of interfacial atoms, thereby improving the interfacial bonding quality.

[0048] The present invention also proposes a copper-clad iron conductive rod, which is prepared according to the above method.

[0049] Traditional composite processes for copper-clad iron conductive rods often face the dilemma of weak interfacial bonding and difficulty in achieving both conductivity. This invention, starting from the synergy of interfacial bonding mechanism and material properties, innovatively solves this problem by introducing a synergistic mechanism of metal transition layer and cold plastic deformation.

[0050] The microscopic metallic transition layer prepared on the surface of the iron core in this invention not only effectively isolates the iron matrix from oxidation but also creates an ideal interface environment for subsequent composite bonding. The multi-pass cold drawing composite process employed is not a simple mechanical reduction of diameter; rather, it uses continuously increasing pressure to induce plastic flow between the copper layer and the iron core at the microscopic level. Under high pressure, the newly formed metal surface overcomes the interface barrier, achieving close contact at the atomic scale and forming a strong and tough bonding interface composed of mechanical interlocking and initial atomic diffusion. This solid-state bonding method completely avoids the defects of the heat-affected zone and the risk of high-temperature oxidation associated with fusion welding, laying a solid foundation for obtaining a highly intact composite interface.

[0051] To further optimize interface performance and coordinate the internal state of the material, this invention employs multi-pass cold drawing followed by annealing. This provides sufficient kinetic energy for the interface atoms to overcome the diffusion barrier, promoting a transformation from mechanical interlocking to a more stable metallurgical bond, significantly enhancing interface bonding strength and airtightness. Simultaneously, it eliminates internal stress accumulated during cold working, restoring the material's toughness. Furthermore, the reducing atmosphere effectively reduces the overall oxygen content of the conductive rod, significantly improving the purity of the conductive channel. The copper-clad iron conductive rod obtained by this invention exhibits high conductivity and high strength.

[0052] This invention establishes a tight process loop, from interface control of the transition layer to solid-state bonding via cold drawing, and then to performance optimization through annealing. This creates a simple, efficient, and reliable fabrication path, ensuring not only superior and consistent product performance but also significant advantages in manufacturing cost and production efficiency. This invention provides a clear and feasible industrial solution to address the core challenges of interface bonding, performance balancing, and cost control in the large-scale industrial application of high-performance copper-clad iron conductive rods. Detailed Implementation

[0053] The technical solution of the present invention will now be described in detail through specific embodiments.

[0054] Example 1

[0055] A method for preparing a copper-clad iron conductive rod includes the following steps: Pretreatment: Take a Q235 low carbon steel bar with a diameter of 20 mm and put it into a mixed aqueous solution of sodium carbonate and trisodium phosphate with a total concentration of 40 g / L. Degrease it at 70℃ for 15 min. Then pickle it in a 12 wt% sulfuric acid aqueous solution at room temperature for 5 min to completely remove the oxide scale. Finally, immerse it in a 6 wt% hydrochloric acid aqueous solution at room temperature for 45 s to activate it. Electroplating: The plating solution is then immediately transferred to an electroplating tank for electroplating. The electroplating conditions are as follows: Watts nickel plating solution is used, the concentration of nickel sulfate in the nickel plating solution is 230 g / L, the pH value of the nickel plating solution is 4.0, the temperature of the nickel plating solution is 55℃, and the cathode current density is 2 A / dm³. 2 The electroplating time is 7 minutes, forming a dense and continuous nickel transition layer with a thickness of about 1.5 μm on the surface of the iron rod, thus obtaining an iron rod with a nickel transition layer on the surface. Copper tube cladding: Using a T2 oxygen-free copper tube with an inner diameter of 20.2 mm and a wall thickness of 4.4 mm (oxygen content <30 ppm), the T2 oxygen-free copper tube is clad onto an iron rod with a nickel transition layer on the surface by a light sliding method (the single-sided gap between the inner diameter of the copper tube and the diameter of the iron rod with a nickel transition layer on the surface is 0.1 mm), to obtain a composite billet; Multi-pass cold drawing composite: The composite blank was subjected to four cold drawing processes to achieve composite bonding and shaping. The drawing rate was 3 m / min, and k was set to 1.2. s The value is 400MPa, and the drawing conditions for each pass are shown in Table 1. This process achieves a strong metallurgical-mechanical bond between copper and iron under huge hydrostatic pressure through precisely controlled plastic deformation, resulting in a composite rod with an outer copper layer thickness of 2.5mm. Annealing: The composite rod was annealed in an atmosphere of ammonia decomposition hydrogen at 425℃ for 45 min, and then cooled to room temperature in the furnace to obtain a copper-clad iron conductive rod.

[0056] Table 1. Drawing conditions for each pass in Example 1

[0057] Example 2 A method for preparing a copper-clad iron conductive rod includes the following steps: The electroplating conditions were as follows: a pyrophosphate copper plating solution was used, with a copper pyrophosphate concentration of 80 g / L, a pH of 8.5, a temperature of 53℃, and a cathode current density of 1.0 A / dm³. 2 The electroplating time was 12 minutes, forming a dense and continuous copper transition layer with a thickness of about 2.8 μm on the surface of the iron rod, resulting in an iron rod with a copper transition layer on the surface; other aspects are the same as in Example 1.

[0058] Example 3

[0059] A method for preparing a copper-clad iron conductive rod includes the following steps: An iron rod with a nickel transition layer on its surface was prepared according to the method of Example 1; Using a T2 oxygen-free copper tube with an inner diameter of 20.2 mm and a wall thickness of 13.0 mm (oxygen content <30 ppm), the T2 oxygen-free copper tube is slipped onto an iron rod with a nickel transition layer on its surface by a light sliding method (the single-sided gap between the inner diameter of the copper tube and the diameter of the iron rod with a nickel transition layer on its surface is 0.1 mm), to obtain a composite billet; The composite blank was subjected to four cold drawing processes to achieve composite bonding and shaping. The drawing rate was 3 m / min, and k was set to 1.2. s The value is 400MPa, and the drawing conditions for each pass are shown in Table 2. This process achieves a strong metallurgical-mechanical bond between copper and iron under huge hydrostatic pressure through precisely controlled plastic deformation, resulting in a composite rod with an outer copper layer thickness of 7.2mm. The composite rod was annealed at 425℃ in an atmosphere of ammonia decomposition hydrogen for 45 min, and then cooled to room temperature in the furnace to obtain a copper-clad iron conductive rod.

[0060] Table 2. Drawing conditions for each pass in Example 3

[0061] Example 4 A method for preparing a copper-clad iron conductive rod includes the following steps: The annealing temperature was 400℃ and the annealing time was 60 min, and other conditions were the same as in Example 1.

[0062] Comparative Example 1 A method for preparing a copper-clad iron conductive rod includes the following steps: After pretreatment, Q235 low-carbon steel bars are directly covered with copper tubes without electroplating, and other procedures are the same as in Example 1.

[0063] Comparative Example 2 A method for preparing a copper-clad iron conductive rod includes the following steps: The thickness of the nickel transition layer is 0.3 μm, and the rest is the same as in Example 1.

[0064] Comparative Example 3 A method for preparing a copper-clad iron conductive rod includes the following steps: The thickness of the nickel transition layer is 8 μm, and the rest is the same as in Example 1.

[0065] Comparative Example 4 A method for preparing a copper-clad iron conductive rod includes the following steps: Adjust the inner diameter of the T2 oxygen-free copper tube so that the single-sided gap between the inner diameter of the copper tube and the diameter of the iron rod with a nickel transition layer on the surface is 0.01 mm, and the rest is the same as in Example 1.

[0066] Comparative Example 5 A method for preparing a copper-clad iron conductive rod includes the following steps: Adjust the inner diameter of the T2 oxygen-free copper tube so that the single-sided gap between the inner diameter of the copper tube and the diameter of the iron rod with a nickel transition layer on the surface is 0.4 mm, and the rest is the same as in Example 1.

[0067] Comparative Example 6 A method for preparing a copper-clad iron conductive rod includes the following steps: The composite preform was prepared according to Example 1. Then, four cold drawing composite processes were performed at a drawing rate of 3 m / min, resulting in a total cross-sectional reduction rate of 20%, yielding a composite rod with an outer copper layer thickness of 3.1 mm. The composite rod was annealed at 425℃ in an atmosphere of ammonia decomposition hydrogen for 45 min, and then cooled to room temperature in the furnace to obtain a copper-clad iron conductive rod.

[0068] Comparative Example 7 A method for preparing a copper-clad iron conductive rod includes the following steps: The composite preform was prepared according to Example 1. Then, four cold drawing composite treatments were performed at a drawing rate of 3 m / min, resulting in a total cross-sectional reduction rate of 55%.

[0069] Because the total cross-sectional reduction rate was too high, far exceeding the plastic limit of the material, work hardening accumulated in the final stage of drawing, leading to fracture and making it impossible to obtain a complete sample.

[0070] Comparative Example 8 A method for preparing a copper-clad iron conductive rod includes the following steps: The annealing temperature was 200℃, the annealing time was 60 min, and other conditions were the same as in Example 1.

[0071] Comparative Example 9 A method for preparing a copper-clad iron conductive rod includes the following steps: The annealing temperature was 600℃ and the annealing time was 60 min, and other conditions were the same as in Example 1.

[0072] The conductive rods of Examples 1-4 and Comparative Examples 1-6 and 8-9 were used for performance testing, and the results are shown in Table 3.

[0073] Interfacial bond strength: Performed in accordance with ASTM D4541 "Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers", and measured using a portable adhesion tester.

[0074] Conductivity: Performed in accordance with GB / T 3048.2-2007 "Test Methods for Electrical Properties of Wires and Cables - Part 2: Test for Resistivity of Metallic Materials", using a double-arm bridge for measurement.

[0075] Tensile strength: Performed in accordance with GB / T 228.1-2010 "Metallic materials, tensile testing - Part 1: Test method at room temperature", and tested on a universal testing machine.

[0076] Repeated bending test: Perform the test according to GB / T 238-2013 "Metallic materials wire repeated bending test method", and record the number of bends until cracks or delamination appear.

[0077] Air tightness: Performed in accordance with GB / T 11813-2008 "Helium Mass Spectrometry Vacuum Leak Detection Method", using helium mass spectrometry leak detection method, and record the leak rate.

[0078] Table 3 Performance test data of conductive rod samples prepared in the examples and comparative examples

[0079] Comparing Example 1 and Comparative Example 1, it was found that: Comparative Example 1 completely omitted the transition layer, which caused the clean copper-iron interface to undergo interdiffusion during subsequent heat treatment, and also made it very easy to generate brittle intermetallic compounds. Due to the huge difference in the thermal expansion coefficients of the two, high residual stress was generated, which ultimately resulted in extremely low bonding strength and interface delamination.

[0080] Comparing Example 1 and Comparative Example 2, it was found that the thickness of the transition layer in Comparative Example 2 was too thin, and its function as a diffusion barrier was incomplete. It could not effectively prevent iron atoms from diffusing into the copper through the thin layer during annealing, forming a local weak bonding region. At the same time, its ability to buffer stress was insufficient, resulting in a bonding strength that was significantly lower than the qualified level.

[0081] Comparing Example 1 and Comparative Example 3, it was found that the thickness of the transition layer in Comparative Example 3 was too thick. Although the bonding strength was acceptable, the resistivity of the nickel transition layer itself was much higher than that of copper. The excessively thick low conductivity layer connected in series in the circuit was like an additional resistor, which significantly reduced the overall conductivity.

[0082] Comparing Example 1 and Comparative Example 4, it was found that the single-sided gap of Comparative Example 4 was too small, resulting in severe mechanical interference during the tube insertion process. The strong friction force would partially scratch or destroy the pre-prepared precision transition layer, causing congenital damage to the interface, thereby deteriorating the bonding strength and airtightness.

[0083] Comparing Example 1 and Comparative Example 5, it was found that the single-sided gap of Comparative Example 5 was too large, which caused the copper tube to be unable to be subjected to uniform and sufficient radial compression during the initial drawing. The interfacial pressure in some areas was insufficient, making it difficult to achieve complete material plastic rheology and atomic-level contact, resulting in uneven bonding and low overall bonding force.

[0084] Comparing Example 1 and Comparative Example 6, it was found that the total cross-sectional reduction rate of Comparative Example 6 was too low. The hydrostatic pressure applied to the copper-iron interface was insufficient to break the surface film and promote close atomic contact between the two sides. The interface only achieved a loose mechanical bond rather than a strong metallurgical bond. Therefore, the bonding strength and airtightness were both unqualified.

[0085] Comparing Example 1 and Comparative Example 8, it was found that the annealing temperature of Comparative Example 8 was too low, resulting in insufficient diffusion kinetic energy for atoms. This made it impossible to effectively achieve interdiffusion of interface elements to enhance bonding, and it was also insufficient to completely reduce the copper oxide on the surface. Therefore, the improvement in bonding strength and conductivity was limited.

[0086] Comparing Example 1 and Comparative Example 9, it was found that the annealing temperature of Comparative Example 9 was too high, which caused a violent interdiffusion reaction at the copper-iron interface, resulting in an excessively thick and brittle intermetallic compound layer. This brittle layer is prone to becoming a crack source when subjected to stress, leading to a sharp drop in bonding strength and brittle peeling. At the same time, the excessively thick compound also increases the electrical resistance.

[0087] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a copper-clad iron conductive rod, characterized in that, Includes the following steps: A copper tube is fitted onto an iron rod with a metal transition layer on its surface, and then a composite rod is obtained by multiple cold drawing processes; then it is annealed to obtain a copper-clad iron conductive rod.

2. The method for preparing the copper-clad iron conductive rod according to claim 1, characterized in that, The iron bar is made of low-carbon steel or low-alloy high-strength steel; preferably, the low-alloy high-strength steel contains chromium and vanadium.

3. The method for preparing the copper-clad iron conductive rod according to claim 1 or 2, characterized in that, The metal transition layer is made of nickel or copper; preferably, the thickness of the metal transition layer is 1-3 μm; preferably, the metal transition layer is prepared by electroplating on the surface of the iron rod.

4. The method for preparing the copper-clad iron conductive rod according to any one of claims 1-3, characterized in that, The copper tube is made of oxygen-free copper; preferably, the oxygen content of the oxygen-free copper is ≤100 ppm.

5. The method for preparing the copper-clad iron conductive rod according to any one of claims 1-4, characterized in that, The single-sided gap between the inner diameter of the copper tube and the diameter of the iron rod with a metal transition layer on its surface is 0.05-0.15 mm; Preferably, the wall thickness of the copper tube is The copper layer thickness of the composite rod is , Preferably, the copper layer thickness of the composite rod is [missing information]. The radius of the composite rod is R. .

6. The method for preparing the copper-clad iron conductive rod according to any one of claims 1-5, characterized in that, The number of cold drawing passes is 3-6; preferably, the total cross-sectional reduction rate is 30-50% during the multi-pass cold drawing composite process; preferably, the cross-sectional reduction rate of the initial pass is 15-20% during the multi-pass cold drawing composite process, and the cross-sectional reduction rate of each subsequent pass decreases to 5-10%.

7. The method for preparing the copper-clad iron conductive rod according to any one of claims 1-6, characterized in that, In the multi-pass cold drawing composite process, the drawing force of each pass. ,in, k For safety factor, k The value ranges from 1.1 to 1.

3. σ The average flow stress of the copper-iron composite material. σ The value ranges from 350 to 500 MPa. A 0 、A 1 These are the cross-sectional areas of the composite rods before and after each pass. Preferably, the drawing rate for each pass is 2-5 m / min.

8. The method for preparing the copper-clad iron conductive rod according to any one of claims 1-7, characterized in that, Annealing is performed in a protective gas atmosphere; preferably, the dew point of the protective gas is ≤-20°C; preferably, the protective gas is hydrogen or hydrogen decomposed from ammonia.

9. The method for preparing the copper-clad iron conductive rod according to any one of claims 1-8, characterized in that, The annealing temperature is 400-500℃ and the annealing time is 30-60 min; preferably, the temperature is increased to 400-500℃ at a rate of 5-15℃ / min.

10. A copper-clad iron conductive rod, characterized in that, A copper-clad iron conductive rod is prepared according to the method described in any one of claims 1-9.

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